This invention relates to porosimeters, more particularly to porosimeters wherein the porous material to be analyzed is first saturated with water so that it may be frozen and thawed in the porosimeter to analyze the porosity of the material.
The pore characteristics of many materials are determinative of the advantageous utility of these materials for specific uses and tasks. For example, the adsorbancy of fine powders in chemicals catalysis is determined by the pore size and size distribution characteristics of the powder, as is the frost resistance of bricks. Therefore, there is a real need for apparatus and methods to determine and measure the pore characteristics of a variety of materials.
One method by which total pore volume and pore-size distribution is estimated is by gas-adsorption isotherms. In this method, pore volume is related to the amount of gas adsorbed on the external surface of the porous material sample in comparison with the amount adsorbed in the pores at a saturation pressure. Problems exist with this method, particularly in interpretation of the resulting measurements.
Another method of estimating porosity is the use of mercury porosimetry which derives pore volume distribution by measuring the cumulative volumes of mercury entering the porous sample material as a function of increasing pressure. This technique is based upon the principle that a minimum pressure is required to force mercury through the pore openings.
Problems can arise using this technique in that damage to the pores may occur with increasing pressure. Additionally, assumptions have to be made regarding contact angle and pore shape.
A related method of using a mercury porosimeter to measure the porosity of a porous material involves measuring the change in electrical resistance of a wire dipped in the mercury to derive the change in the volume of the mercury as pressure is increased and decreased.
As is evident, mercury porosimetry requires complex equipment and integrity of the system so that the pressure in the system can be varied accurately to derive maximum information.
Other methods exist utilizing various processes for estimating pore size and size distribution, but they basically follow the same general techniques of the methods described above and are therefore subject to the same problems.
The method of forcing mercury into the pores of the materials by increasing pressure works well for materials having nearly cylindrical pores and predictable contact angles for mercury, however, few materials exist in such a perfect state. Additionally, conventional mercury porosimetry data curves are difficult to interpret, usually having a hard to interpret hysteresis between curves plotted for pressurization and depressurization.
In order to avoid complications due to this hysteresis, attempts have been made to intrude the sample twice to more accurately determine the distribution of uniform pores, but this method is subject to contamination of the pores by the mercury and chemisorption of the mercury by the sample.
Therefore, it is an object of this invention to provide an ice porosimeter which accurately and efficiently measures pore characteristics of a porous material.
A further object of this invention is to provide an ice porosimeter from which can be derived accurate estimations of pore volume, pore size, pore-size distribution, and specific surface of porous materials, making use of changes in any property of a system which contains such a material, as a result of phase transitions taking place in it as temperature in this system changes.
A further object of this invention is to provide an ice porosimeter which can also accurately estimate the radius of pore constrictions during the freezing process.
Another object of this invention is to provide an ice porosimeter which utilizes the phase transitions of water to more accurately measure the pore characteristics of a porous material.
Another object of this invention is to provide an ice porosimeter which is simple in construction, simple to use, and simple to interpret.
A further object of this invention is to provide an ice porosimeter which is economical and efficient.
Additional objects, features, and advantages of the invention will become apparent with reference to the accompanying specification and drawings.